Behind-Outcrop Cores Tied to Adjacent Cliff Sections — The Architecture of the Upper Ross Deepwater Fan to Slope Transition, Western Ireland

The Carboniferous Ross Formation in the Clare Basin, western Ireland, is a particularly well-exposed, deepwater fan system that has been extensively used for industry and academic training and as an analogue for reservoir characterisation purposes. A behind-outcrop coring program currently underway has now acquired >700 m of core and associated wireline logs from five sites on the Loop Head peninsula. The aim is to provide subsurface data to compliment the training resource in West Clare, and give new insight into the bed and larger-scale architecture of an icehouse-forced, prograding fan system similar to Miocene and younger examples in the subsurface elsewhere.

Split cores from two of the cores (09-CE-UCD-01 and -02) have been logged in detail and linked to adjacent cliff and foreshore sections and to photo-mosaics of the cliffs taken from the sea - both boreholes were drilled on the north side of the Loop peninsula east of Bridges of Ross and they core the uppermost (and hence inner and slope-adjacent) part of the progradational Ross system and its upward transition into the Gull Island slope deposits.

A correlation panel linking the cores, outcrop data and photo-panels extends 8 km laterally and captures the upper 175 m of the Ross and the basal Gull Island formations. The correlation is tied using laterally-continuous, metre-scale condensed sections that are recognised in both the cliffs and the boreholes. Other distinctive large scale architectural elements have been identified and mapped. These include the Ross Slump and a number of other mud- and sand-prone slumped horizons at deeper stratigraphic levels. Lateral changes in the degree of channelization are also highlighted by the panel. The new core data allow for a detailed quantitative analysis of the vertical variation in bed types within the framework of high-frequency cycles. A bed catalogue has been developed to reflect this high resolution data. Building from bed scale upwards, the correlation records in unprecedented detail the intercalation between sheet-form turbidites, hybrid event beds, locally developed channel fills and complex slump and slide units reflecting the increasingly unstable and erosion-prone setting towards the top of the Ross.  

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California